Device for catalytic purification of exhaust gases

ABSTRACT

Catalyzers for purification of exhaust gases are disclosed including a housing, an inlet for supplying the exhaust gases to the housing, a first catalyzer within the housing adjacent to the inlet and a second catalyzer within the housing downstream of the first catalyzer, the first catalyzer having a smaller cross-sectional area than the second catalyzer, and the inlet being angled with respect to the longitudinal axis of the first catalyzer.

FIELD OF THE INVENTION

The present invention relates to a catalytic exhaust gas purificationarrangement.

BACKGROUND OF THE INVENTION

Catalytic exhaust gas purifiers are often used in motor vehicles inorder to purify the exhaust gases from the vehicle's engine. However,present catalytic converters (catalyzers) are not able to operate atfull purification efficiency in connection with cold-starting of avehicle. This problem can be overcome by arranging an additional,electrically-heatable start catalyzer in front of the ordinarycatalyzer. By heating up the start catalyzer electrically, the warm-uptime for the ordinary catalyzer can be shortened, which results inimproved purification efficiency during cold starts. Such a catalyzerarrangement is shown in International Patent No. WO 80/10470.

A problem which occurs in connection with an electrically-heatable startcatalyzer is that it requires a powerful electrical supply in order tobe activated. This can, for example, be achieved by arranging anadditional battery in the vehicle, which is however unnecessarilyexpensive and complicated. It is therefore desirable to have a catalyzerarrangement which is not dependent on an electrical supply, but whichstill produces a shortening of the main catalyzer's "ignition" time (theso-called "light-off" time), i.e. the time which elapses from startingthe engine until the catalyzer is working at optimal purificationefficiency. This should, in such a case, result in improved purificationefficiency of the entire catalyzer arrangement.

In connection with conventional catalyzers, there is an additionalproblem in that the incoming exhaust gases impinge directly onto thecatalyzer. This produces a turbulent flow immediately in front of thecatalyzer, which leads to inefficient operation of the catalyzer as wellas a comparatively high back-pressure, which is a disadvantagecompounding the reduction in the efficiency of the catalyzer. One way ofsolving this problem is to direct the exhaust gases at an angle to thecatalyzer, for instance in accordance with the disclosure in EuropeanPatent No. 420,462. This arrangement, however, presents a disadvantagein that it has relatively poor flow characteristics, since not only theinlet but also the outlet are angled with respect to the catalyzer.

A main object of the present invention is to solve the aforementionedproblems and provide an improved arrangement for catalytic exhaust gaspurification, in particular for shortening the light-off time of such anarrangement.

An additional object of the present invention is to achieve a correctmeasurement of the conversion efficiency of the aforementioned catalyzerarrangement, in order to provide information for a diagnosis of itsoperation. This allows an indication, e.g. in the form of a warninglight, which warns the vehicle driver that the catalyzer is defectiveand has to be replaced.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other objects havenow been realized by the invention of apparatus for the catalyticpurification of exhaust gases which comprises a housing, an inlet forsupplying the exhaust gases to the housing, the inlet having a first enddistal from the housing and a second end proximate to the housing, afirst catalyzer unit having a first cross-sectional area located withinthe housing adjacent to the second end of the inlet, the first catalyzerunit having a longitudinal axis, and a second catalyzer unit having asecond cross-sectional area located within the housing downstream of thefirst catalyzer unit, the first cross-sectional area being less than thesecond cross-sectional area, the second end of the inlet being disposedat an angle with respect to the longitudinal axis of the first catalyzerunit. Preferably, the apparatus includes a third catalyzer unit locatedwithin the housing downstream of the second catalyzer unit.

In accordance with one embodiment of the apparatus of the presentinvention, the second catalyzer unit has a substantially ovalcross-section.

In accordance with another embodiment of the apparatus of the presentinvention, the first catalyzer unit has a substantially circularcross-section.

In accordance with one embodiment of the apparatus of the presentinvention, the ratio of the size of the first catalyzer unit to thesecond catalyzer unit is between about 0.5:3 and 2.9:3, and preferablyis about 2:3.

In accordance with another embodiment of the apparatus of the presentinvention, the first catalyzer unit includes a plurality oflongitudinally extending channels and the second catalyzer unit has alongitudinal axis, and the direction of the longitudinally extendingchannels of the first catalyzer unit substantially coincides with thelongitudinal axis of the second catalyzer unit.

In accordance with another embodiment of the apparatus of the presentinvention, the apparatus includes a first lambda sensor located upstreamof the first catalyzer unit and a second lambda sensor locateddownstream of the first catalyzer unit.

In accordance with another embodiment of the apparatus of the presentinvention, the first catalyzer unit has a first symmetry with respect tothe longitudinal axis and the second catalyzer unit has a secondsymmetry with respect to the longitudinal axis of the catalyzer unit,and the longitudinal axis of the first catalyzer unit is displacedperpendicular with respect to the longitudinal axis of the secondcatalyzer unit.

In accordance with another embodiment of the apparatus of the presentinvention, the angle of the inlet with respect to the longitudinal axisof the first catalyzer unit is between about 10° and 40°, and preferablyabout 20°.

It has thus been found that by arranging a relatively small firstcatalyzer upstream of the ordinary catalyzer and by permitting theexhaust gases to be incident at an angle to this first catalyzer, aneffective purification effect on the entire catalyzer arrangement isachieved.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention may be more fully appreciated with reference tothe following detailed description, which, in turn, refers to theFigures, in which:

FIG. 1 is a side, elevational view of apparatus in accordance with thepresent invention;

FIG. 2 is a top, elevational view of the apparatus shown in FIG. 1;

FIG. 3 is a side, elevational, sectional view of the apparatus shown inFIG. 2 taken along line A--A thereof;

FIG. 4 is a partial, side, partially sectional, enlarged view of aportion of the apparatus shown in FIG. 1;

FIG. 5 is a side, elevational view of another embodiment of theapparatus of the present invention;

FIG. 6 is a side, elevational view of apparatus similar to the apparatusshown in FIG. 1 provided with lambda sensors for diagnosing theoperation of the catalyzer arrangement;

FIG. 7 is a top, elevational view of another embodiment of the apparatusof the present invention; and

FIG. 8 is a side, elevational, cross-sectional view of the apparatusshown in FIG. 7 taken along line B--B thereof.

DETAILED DESCRIPTION

Referring to the Figures, in which like reference numerals refer to theelements thereof, FIG. 1 shows a side view of an arrangement inaccordance with the present invention. According to a preferredembodiment, the arrangement comprises a catalytic exhaust gas purifierwith a first monolithic catalyzer unit 1. Downstream of the firstcatalyzer 1 there is a main catalyzer which comprises a secondmonolithic catalyzer 2 and a third monolithic catalyzer 3.

The first catalyzer 1 is preferably composed of a metallic catalyzerwhich has a circular cross-section with about 98 mm diameter and alength of between 74 and 90 mm, as well as a cell density of the orderof 200 cpsi (cells per square inch). A metallic catalyzer has theadvantage that it has a considerably larger catalytic active area than aceramic catalyzer. Another advantage is that the energy is transportedquickly from this to the second catalyzer 2. The second catalyzer 2 andthe third catalyzer 3 are preferably composed of similar ceramiccatalyzers of the monolithic, three-way catalyzer type. Other types ofcatalyzers are also possible. The two catalyzers, 2 and 3, are formed sothat their size and cell-density are substantially the same, while otherparameters such as length and type of catalytic coating can bedifferent.

An inlet channel 4 is arranged upstream of the first catalyzer 1. Theexhaust gases flow through the inlet channel 4 from a combustion engineof conventional type (not shown). The part of the inlet channel 4 whichlies closest to the first catalyzer 1 is somewhat widened, which givesan optimal flow of the exhaust gases through the inlet channel 4. Theinlet channel 4 presents an angle with respect to the longitudinaldirection of the catalyzers, 1, 2 and 3, which lies between about 10°and 40°, preferably about 20°. The complete arrangement is enclosed in acommon casing 5 of metal. The arrangement also includes an outletchannel 6, through which the exhaust gases flow when they have passedthrough all of the catalyzers, 1, 2 and 3. The outlet channel 6 ispreferably formed as a straight, relatively long conical section. Thisarrangement is advantageous with respect to the flow characteristics ofthe exhaust gases at the outlet of the catalyzer arrangement.

FIG. 2 shows a view from above of the arrangement according to thepresent invention. From this Figure, as well as from FIG. 3 which is across-sectional view along section A--A in FIG. 2, it is clear that thesecond catalyzer 2 and the third catalyzer 3 have a substantially ovalcross-section.

The complete function of the catalyzer arrangement will now bedescribed. The first catalyzer 1 has a considerably smallercross-sectional area than the second and third catalyzers, 2 and 3. Theratio between the size of the cross-sectional area of the firstcatalyzer 1 and the second catalyzer 2 is between about 0.5:3 and 2.9:3,preferably about 2:3. The first catalyzer 1 also has a relatively smallvolume. This means that it is heated up relatively quickly due to theheat from the exhaust gases and the heat from the catalytic reaction inthe catalyzer 1. Thus, a catalytic reaction will be started up quicklyin the first catalyzer 1.

Since the cross-sectional area of the first catalyzer 1 is less than thecross-sectional area of the following second catalyzer 2, the exothermicheat of the exhaust gas flow out of the first catalyzer 1 will beconcentrated to a certain extent in the second catalyzer 2. This means,in turn, that a particular central part of the second catalyzer 2 willbe heated up relatively quickly, whereby the catalytic reaction can alsostart up more rapidly in the second catalyzer 2. The second catalyzer 2is a ceramic catalyzer which has a lower thermal conductivity than thefirst catalyzer 1, which is a metallic catalyzer. This contributes to anefficient operation of the entire catalyzer arrangement.

As can be seen in FIGS. 1 and 2, the inlet channel 4 is angled withrespect to the longitudinal axis of symmetry of the first catalyzer 1.This means that the cross-sectional area through the inlet channel 4 isless than the cross-sectional area for the frontal surface of the firstcatalyzer 1, onto which the exhaust gases are incident. In this manner,a turbulent flow in front of the first catalyzer 1 is avoided andinstead a laminar flow of the exhaust gases through the inlet channel 4if obtained up until they reach the first catalyzer 1.

When the flowing exhaust gases reach the first catalyzer 1 they will"collide" with the walls of the catalyzer 1. This process is shown inFIG. 4, which is an enlarged partial view of a portion of the inletchannel 4 and the first catalyzer 1. The first catalyzer 1 is, in aknown manner, formed with a number of longitudinal channels, of whichthree channels, 7, 8 and 9, are shown in FIG. 4. According to thisembodiment, the channels, 7, 8 and 9, are substantially straight, i.e.they follow the longitudinal direction of the catalyzer 1, but they canalso have another form, e.g. a curved shape or a zigzag shape. Theexhaust gas flow is shown schematically with arrows, 10, 11 and 12,respectively. The exhaust gas stream/flow, as mentioned above, has alaminar flow through the inlet channel 4. When the exhaust gas flow isincident on the channels, 7, 8 and 9, the laminar flow effectively goesthrough a transition to a turbulent flow. This is indicated in FIG. 4with "turbulent" flow lines, 13, 14 and 15. The transition from laminarto turbulent flow occurs as a result of the inlet channel 4 beingangled, both in the height direction and the sideways direction, withrespect to the longitudinal direction of the first catalyzer 1. Theturbulent flow gives rise to a rapid heating of the first catalyzer 1,due to which its catalytic reaction can start quickly.

Further downstream in the first catalyzer 1, the turbulent flow againgoes through a transition to a laminar flow.

FIG. 5 shows a side view of an alternative embodiment of the presentinvention. As in the aforementioned embodiment, it comprises acomparatively small first catalyzer 1 and a main catalyzer comprising asecond catalyzer 2 and a third catalyzer 3. Additionally, it comprisesan inlet channel 4 which is slanted with respect to the firstcatalyzer 1. In this manner, a zone having turbulent flow is obtained atthe inlet to the first catalyzer 1, similar to that which has beendescribed above. This alternative embodiment also comprises a casing 5with an intermediate portion 16 which is arranged between the firstcatalyzer 1 and the second catalyzer 2. The first catalyzer 1 issomewhat slanted with respect to the intermediate portion 16, i.e. thelongitudinal axis 20 of symmetry of the first catalyzer 19 forms anangle with respect to the longitudinal axis 20 of symmetry of theintermediate portion 16. Additionally, the intermediate portion 16 isformed so that its longitudinal axis of symmetry forms an angle to thelongitudinal axis of symmetry of the second catalyzer 2. In this manner,a zone with turbulent flow is also formed at the inlet to the secondcatalyzer 2. This assists in giving an increased efficiency of theentire catalyzer arrangement by the second catalyzer 2 having a shorterlight-off time.

FIG. 6 is a side view of a further embodiment of the present inventionwhich is similar to that shown in FIG. 1, but which further comprisestwo lambda sensors 17 and 18, which can be used for measuring the degreeof conversion of the catalyzer arrangement. A lambda sensor is a type ofsensor which produces an electrical signal which varies with the oxygencontent of the exhaust gases. A first lambda sensor 17 is arranged infront of the first catalyzer 1 and a second lambda sensor is arrangedafter the third catalyzer 3.

Both of the lambda sensors, 17 and 18, are also connected to an analyzerunit (not shown) which, on the basis of signals from the lambda sensors,17 and 18, can calculate a value for the degree of conversion of thecatalyzer arrangement, i.e. its purification ability. In the event thatthe analysis unit determines that the purification ability of thecatalyzer arrangement is much too low, an alarm signal can be activated.Such a signal can comprise e.g. a warning light on the motor vehicle'sinstrument panel. The driver of the vehicle can thus be made aware thatthe catalyzer arrangement needs to be replaced.

A special problem can arise if the catalytic active coating of thecatalyzers has a high oxygen storage capacity, which can sometimes bethe case with modern catalyzers. This leads to the following problemarising during a diagnosis with the aid of the lambda sensors, 17 and18. If the second lambda sensor 18 is placed in the outlet channel 6(see FIG. 6), and the catalyzers, 1, 2 and 3, arranged upstream have ahigh oxygen storage capacity, only a small amount of oxygen will beavailable at the second lambda sensor 18. This means that the signalfrom the second lambda sensor 18 becomes unstable and can vary greatly.In the worst case, the signal can be interpreted by the analyzer unit asbeing a signal indicating a malfunctioning catalyzer. In order to solvethis problem, the second lambda sensor 18 can be arranged in a differentlocation rather than after the third catalyzer 3, e.g. between the firstcatalyzer 1 and the second catalyzer 2 or between the second catalyzer 2and the third catalyzer 3. In this manner, reliable measurements can beobtained.

In the event that it is desired to place the second lambda sensor 18 asclose as possible downstream of the first catalyzer 1, problems canarise concerning the space which is available in the vehicles. In orderto solve this problem, the first catalyzer 1 can be arranged somewhatdisplaced in the sideways direction, i.e. with respect to thesymmetrical longitudinal axis of the second catalyzer 2. Thisarrangement is shown in FIG. 7.

The function of this arrangement is ensured as long as the firstcatalyzer 1 is not displaced further out to the side than the pointwhere its outlet flow ends up inside the oval cross-section of thesecond catalyzer 2. FIG. 8, which shows a cross-section along line B--Bin FIG. 7, defines a possible placement of the first catalyzer 1 withrespect to the second catalyzer 2.

What is stated above concerning the arrangement of the lambda sensors,17 and 18, can of course also be applied in connection with theembodiment which is shown in FIG. 5.

The present invention is not limited to the embodiments described above,but can be varied within the scope of the appended claims. For example,different types of catalyzer can be used. Moreover, the catalyzers, 1, 2and 3, can have different dimensions and shapes.

The main catalyzer can constitute a single catalyzer instead of the twoabove-mentioned catalyzers, 2 and 3. Moreover, the first catalyzer 1 canbe combined with a so-called HC-trap or an electrically heatablecatalyzer, e.g. an electrical start-catalyzer or a gas burner. In thismanner, an additional improvement of the purification efficiency can beachieved.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

We claim:
 1. Apparatus for the catalytic purification of exhaust casescomprising a housing, an inlet for supplying said exhaust gases to saidhousing, said inlet having a first end distal from said housing and asecond end proximate to said housing, a first catalyzer unit having afirst cross-sectional area located within said housing adjacent to saidsecond end of said inlet, said first catalyzer unit having alongitudinal axis, and a second catalyzer unit having a secondcross-sectional area located within said housing downstream of saidfirst catalyzer unit, said first cross-sectional area being less thansaid second cross-sectional area, said second end of said inlet beingdisposed at an angle with respect to said longitudinal axis of saidfirst catalyzer unit.
 2. The apparatus of claim 1 including a thirdcatalyzer unit located within said housing downstream of said secondcatalyzer unit.
 3. The apparatus of claim 1 wherein said secondcatalyzer unit has a substantially oval cross-section.
 4. The apparatusof claim 1 wherein said first catalyzer unit has a substantiallycircular cross-section.
 5. The apparatus of claim 1 wherein the ratio ofthe size of said first catalyzer unit to said second catalyzer unit isbetween about 0.5:3 and 2.9:3.
 6. The apparatus of claim 5 wherein saidratio of said size of said first catalyzer unit to said second catalyzerunit is about 2:3.
 7. The apparatus of claim 1 wherein said firstcatalyzer unit includes a plurality of longitudinally extending channelsand said second catalyzer unit has a longitudinal axis, and wherein thedirection of said longitudinally extending channels of said firstcatalyzer unit substantially coincides with the longitudinal axis ofsaid second catalyzer unit.
 8. The apparatus of claim 1 including afirst lambda sensor located upstream of said first catalyzer unit and asecond lambda sensor located downstream of said first catalyzer unit. 9.The apparatus of claim 1 wherein said first catalyzer unit has a firstsymmetry with respect to said longitudinal axis and said secondcatalyzer unit has a second symmetry with respect to said longitudinalaxis of said second catalyzer unit, and wherein said longitudinal axisof said first catalyzer unit is displaced perpendicularly with respectto said longitudinal axis of said second catalyzer unit.
 10. Theapparatus of claim 1 wherein said angle of said inlet with respect tosaid longitudinal axis of said first catalyzer unit is between about 10°and 40°.
 11. The apparatus of claim 10 wherein said angle of said inletwith respect to said longitudinal axis of said first catalyzer unit isabout 20°.